A governor is a device used to control engine fueling of a mobile machine based indirectly on operator input. In particular, the operator of the machine may not directly control fueling. Instead, the operator may only indicate a desired engine speed (e.g., via throttle pedal position), and the governor may adjust engine fueling to maintain the desired engine speed regardless of fluctuations in load placed on the engine. For example, when the load increases (e.g., when the machine encounters an incline), the engine could be caused to lug due to the increased load. In this example, assuming the operator maintains the same throttle pedal position, the governor automatically increases fueling to maintain the desired engine speed throughout the incline. Likewise, when the load decreases (e.g., when the machine encounters a decline), the engine could overspeed due to the load reduction. In this example, the governor automatically decreases fueling.
While a speed governor (i.e., a governor that adjusts engine fueling based on engine speed) may perform satisfactorily in some situations, it may be undesired in other situations. For example, there may be situations when the operator is not concerned with the speed of the engine and instead wants only to maintain a specific torque at wheels (a.k.a., rimpull torque) of the machine regardless of fluctuations in engine speed. In these situations, the speed governor may not provide the desired level of control.
Another type of governor is known as a torque governor. A torque governor is configured to adjust engine fueling based on operator input indicative of desired rimpull torque. For example, the operator may depress the throttle pedal indicating a desired percentage of a maximum available torque be applied to the wheels of the machine. The governor detects and/or determines the actual torque being directed from the engine to the wheels, and selectively adjusts fueling based on the difference between the desired and actual torques.
Although a torque governor may provide an added level of machine control to the operator, it may also be problematic in some situations. For example, if the operator were to suddenly request a significant amount of hydraulic power from the machine (e.g., via fast and/or high-force lifting of a work tool) when the machine's engine is being fueled based on desired rimpull torque, the engine would lug due to the sudden increase in load for the same amount of fuel. When the engine lugs, the hydraulic system of the machine might not respond properly.
One exemplary attempt to improve machine operation is disclosed in US Patent Publication No. 2012/0310493 (the '493 publication) of Fukuhara et al. that published on Dec. 6, 2012. Specifically, the '493 publication discloses a work vehicle having an engine, a travel device, a hydraulic pump, a work implement, a torque converter device, and a controller. The torque converter device includes a torque converter and a lockup clutch. The controller is configured to switch the lockup clutch from a connected state to a non-connected state when a load increases on the work implement. By switching the lockup clutch to the nor-connected state, the total load on the engine may decrease, thereby inhibiting lugging of the engine due to the sudden load increase on the work implement.
Although the work vehicle of the '493 publication may experience a decrease in engine lugging and/or have improved hydraulic response during simultaneous travel and tool use, it may be problematic. In particular, the work vehicle may experience a loss of efficiency when operating with the lockup clutch in the non-connected state during torque-governing of the engine. In particular, some losses will be experienced during disconnect of the lockup clutch. And even though the load on the engine may be reduced, fueling based on torque may not fully take into account the work implement load. Thus, the engine may still lug to some degree, which further reduces machine efficiency.
The disclosed power system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.